Solar Power, Solar Energy, Renewable Energy Consultants

Offgrid Solar PV System Calculator

Energy and Battery Calculations

Step 1 - How much power needed per day?

Total Watt Hours per day:

Tip: This is the total amount of energy you require over the course of the day but expressed in watts. If you use an average of 10kW/h per day, you are using 10 000watt hours perday.

Tip2: Another way to get to this figure is by looking at your monthly energy bill. Take the total number of kW/h (also called units) and divide it by 30 or the number days (if on the bill). This will give you a daily average. Multiply that figure by 1000, and you have your watt hours:)

Example: 385kW/h per month / 30 = 12.84kW/h x 1000 = 12840watt hours

Step 2 - System Autonomy

How many days of backup power do you want in case of cloudy/rainy days?

Tip: Batteries are very expensive, if you have eskom or an existing generator it is sometimes better to use less batteries and a Bi Directional Inverter.The inverter will use battery first and then draw of Eskom or a generator when battery power is low.

Tip: Typical values for rainy day calcs are 1 or 2 days but it really depends on the area.


Battery Bank Capacity:

Note: A 10% efficiency loss has been included on the value below:)

watt hours

Select a battery bank voltage:

Tip: Voltage guidelines - 0 - 3000w = 12v, 3000w - 6000w = 24v, 6000w or greater = 48v

Tip: The rules are flexible, the above is just a guideline

Battery Bank Capacity: amp hours

Find the right batteries for your needs here.

Solar Panel/Controller Sizing

This calculator helps you size the solar panel(s) and charge controller(s) needed for your system.

Step 1: Hours of Sun

You need to determine the average number of sun hrs per day.

Manually enter the average sun-hours for your location.


Tip: In general we would make this value 5.5hours as its the best balance between summer and winter. In more arid regions and hotter locations you can increase this to 6 or 6.5

Tip2: If you really want to get accurate about this and would like some more information of your potential generation check out the following link Solar GIS

Step 2: - Peak System Watts

The total wattage of Solar Panels that you need is:

Note: The value below includes 15% efficiency losses

Watts, or kilowatts

Step 3: - Module and Regulator Info

How many solar panels do you need? That depends on the panel you choose.

Select the wattage of the panel your interested in, and see the results below:

watts per panel

IMPORTANT NOTE ON REGULATORS: GW Store makes use primarily of MPPT (Maximum power point tracking) Regulators, only for low budget, application based or really small systems will we use PWM style regulators.

Tip: If you need any assistance with the above points please contact us for advise.


You will need panels for a total of watts.

You will need a charge controller that can handle at least amps

Tip: The above amperage is if you configure the panels in parallel, using an MPPT allows you to configure series connections and keep the amperage low. Please contact us for more information on this topic:)

Find a solar panel that fits your needs here.

Find a charge controller that fits your needs here.

Find an inverter that fits your needs here.

Sizing a charge controller can be complex, the above answer is a conservative estimate. Please feel free to call us to find a more accurate fit for your needs.

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